The present invention relates generally to the field of tracking and/or guiding a boring tool to an underground location using an electromagnetic locating signal and, more particularly, to a system and method which provides for guiding the boring tool to any selected location within an underground region. The target location is unconstrained with respect to any system component geometric arrangements so long as the receiving position is within a receiving range of the boring tool.
One early approach taken by the prior art in tracking a boring tool employs accelerometer and magnetometer sensors in the boring tool. Information is sent to an above ground display through the use of a cable to display pitch and yaw information. In one improvement, the pitch and yaw angles of the boring tool are integrated to estimate the position of the boring tool. It should be appreciated that boring tool position relative to a target is not available in this system Moreover, accumulation of pitch and yaw measurement errors adversely influences the estimated boring tool position.
Another, more recent, approach taken in the prior art, with regard to guiding an in-ground boring tool, embodies a “homing” configuration. In such a configuration, the boring tool homes-in on a receiving position at which a receiver is located. Homing configurations are generally incapable of homing-in on anything other than the receiving position itself. That is, the target of the boring tool is necessarily limited to the position of the receiver. In one improvement, U.S. Pat. No. 4,881,083 (hereinafter the '083 patent) describes a homing configuration wherein the boring tool homes-in on a vertically oriented line extending through the receiver, in one embodiment, or homing in on the receiver itself, in another embodiment. In accordance with the former embodiment (see FIG. 1 of the '083 patent), the receiver is positionable above a pit for purposes of drilling to some previously underground point on the vertical line below the previous surface of the ground. The system, however, does nothing with respect to monitoring the depth of the boring tool. The depth of the boring tool must be independently established or controlled for the boring tool to properly emerge in the pit. In the latter embodiment (see FIG. 8 of the ('083 patent) and consistent with the prior art in general, the system is incapable of doing any thing other than homing on the receiving position. That is, no target other than the receiving position is possible.
A marked improvement over the general state of the prior art is described as one aspect of U.S. Pat. No. 6,250,402 (hereinafter the '402 patent) which is co-assigned with the present application and which is incorporated herein by reference. In contrast with the prior art, the '402 patent provides for steering a boring tool to specified depth target locations that are directly below the receiver (see FIG. 9 of the '402 patent). As described at column 27, lines 18-20 of the '402 patent, however, even this technique is limited in that the target may not be positioned beyond or in front of the receiver. It should also be appreciated that the target may not be positioned to the side (i.e., laterally displaced) of the receiver.
The present invention serves to remove the foregoing constraints with respect to the prior art while providing still further advantages, as will be described.